1. Field of the Invention
The present invention relates to a device for changing the difference in the brightness, saturation or hue on the screen of a display device 10 disposed in the cabin of a construction machine.
2. Related Art
The cabin of the construction machine is provided with the display device. The display device has a display screen composed of a background portion and a display portion. The display portion is exemplified by bar graphs for indicating numerals such as the residual of a fuel, the water temperature, the oil temperature, the oil pressure or the battery voltage, and by caution marks for indicating abnormal conditions. Here, the “caution marks” imply the aforementioned abnormal conditions in a narrow sense. However, the “caution marks”, as termed herein, imply a wide sense containing a pilot indication such as the parking brake indication or the preheat indication, or a message indication (in letters) . The operator can be informed of the internal state of the construction machine or an abnormal state having occurred in the construction machine by monitoring the display portion on the screen. When the caution mark or marks are turned ON, the operator can recognize the abnormality of the construction machine.
FIG. 2A is a perspective view showing the exterior of a cabin 40 of the construction machine. FIG. 2B shows a monitor panel 10 disposed inside of the cabin 40.
The cabin 40 of the construction machine is surrounded by wide glass areas at its front and back and at its right and left so that a wide field of view is retained. This retention is made to improve the working efficiency and the safety of the construction machine.
On the other hand, the monitor panel 10 is not surrounded by the dash board or the like but is exposed to the outside. This is because an excessive equipment in the cabin 40 will obstruct the field of view.
Here, the cabin 40 shown in FIG. 2A is provided with a roof and with glass shields on its front and back and on its right and left. In another mode, the cabin is provided with neither roof nor glass shield or with a glass shield only on the righthand side (as located on the side of the monitor panel 10, as shown).
In the daytime works, the construction machine is accompanied by the following problems.
At the daytime, the inside of the cabin 40 is exposed directly to the daylight, and so is the display screen 30 of the monitor panel 10. Then, the display screen 30 is not clear in contrast among a background portion 31, bar graphs 32 and caution marks 33 so that it reduces the visibility. This visibility reduction is serious especially in the display screen 30 in the construction machine having no roof in the cabin.
On the other hand, the construction having the glass shields around the cabin 40 is accompanied by the following problems when it is operated at the nighttime.
At the nighttime, the display screen 30 is easily reflected on the glass shields around the cabin 40 by the light emitted from the display screen 30 of the monitor panel 10. These reflections on the display screen 30 of the cabin 40 at the nighttime are caused by the difference between the illuminances of the exterior and the interior of the cabin 40. The images of the display screen 30, as reflected on the glass shields, will obstruct the field of view of the operator to raise a problem that the safe maneuvering is troubled.
If the luminance of the display screen 30 is lowered, the problem of the reflection of the display screen 30 on the glass shields can be solved, but the visibility of the display screen 30 is lowered.